The current treatment of serious retinopathy of prematurity (ROP) requires accurate diagnosis of plus disease to optimize outcome.1 With increasing use of digital imaging to document or screen for the presence of serious retinopathy, the reliability and reproducibility of images collected needs to be carefully examined.2 This may be especially important when a contact camera is used such as the RetCamII (Clarity Medical Systems, Pleasanton, CA, USA), which may compress the eye, thus potentially influencing retinal blood flow and affecting evaluation of the presence of plus disease in the digital image. During routine diagnostic examinations, we observed how unintentional elevation of intraocular pressure by compression with the RetCam hand-held lens and report this finding that has the potential for changing the appearance of plus disease.

Case report

A male infant born at 27 weeks of gestation and birth weight of 800 g was transferred to our hospital for ROP treatment at 35 weeks postmenstrual age. Stage 3 ROP with plus disease was documented using indirect ophthalmoscopy. However, fundus images taken by an experienced photographer 1 h later using the RetCamII failed to show vascular abnormalities in the posterior pole sufficient to be called plus disease. Although the diameter of the vessels appeared to be decreased, some arterioles nearly vanished (Figure 1a).

Figure 1
figure 1

(a) Initial examination: Zone 2 Stage 3, with ‘subtle’ arterial components, note the absent blood column at the optic disc (gray arrow) and whitening of the underlying retina, which is larger than in Figure 1b (black arrows). (b) Second examination: Zone 2, threshold disease, dilatation and tortuosity of venules and arterioles in four quadrants, multiple shunts and less retinal whitening (black arrows).

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Imaging was repeated by a pediatric ophthalmologist within 30 min and by carefully positioning the lens of the RetCam within the viscous material that had been applied to the corneal surface and not touching the cornea, she obtained pictures that clearly showed plus disease with wide vessels and vessel tortuosity (Figure 1b). By applying more pressure to the camera, it was possible to repeat the artifacts.

All images were then reviewed. In addition to the initial findings, absence of the arterial blood column on the optic nerve was noticed, and the area of retinal whitening in the first picture (Figure 1a) was larger than in the second one (Figure 1b). To verify the observations, quantification with Retinal Image multiScale Analysis (RISA) was performed (Figure 2).3 The vessels were narrower in the image with the compression artifact than in the subsequent images. Those findings confirm the impression of a less severe picture of plus disease in Figure 1a.

Figure 2
figure 2

Retinal vascular tree analysis using RISA software. (a) Initial examination: with ‘subtle’ arterial changes at lower temporal inferior quadrant vessels. (b) same branch tree analysed when this picture was taken with no RetCam handheld lens pressure was applied upon the eye. Note how arterial diameter (D), expressed in pixels, consistently decreases when pressure is applied over the eye.

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Comments

Variations in pressure induced by inadvertent indentation with the RetCam lens could compress, decrease intra-arterial diameter or even collapse retinal vessels.4 Evaluation of images of plus disease may then be misinterpreted giving a false-negative result, with a subsequent delay detection of serious retinopathy. Careful attention to technique is essential to eliminate blanching of the retina or absence of the arterial blood column at the nerve head that might indicate excessive pressure during imaging.